Taleyarkhan has been cleared, but repeating his experiments has proven to be …

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Bubble fusion burst onto the scene in 2002 when a team of researchers observed large neutron fluxes from deuterated materials in sonoluminescence experiments. Sonoluminescence is the production of light from acoustically excited liquids. The strong acoustic wave first decompresses the liquid, which allows a gas to form. The acoustic wave then strongly compresses the gas bubble, heating it to the point where the gas can ionize and glow. The bubble eventually collapses in on itself and disappears. A lot of research has gone into learning about these bubbles, and whether the pressures and temperatures get sufficiently high for fusion.

Although bubble fusion was thought to be possible, other researchers in the field were astounded by the amount of neutrons Taleyarkhan reported. Since that time, there have been a number of allegations, from departmental shenanigans through to faking data—the reported spectrum of neutrons was identical to that of a particular radioactive element. In response, Purdue University placed Taleyarkhan on leave and conducted an internal inquiry into the propriety of his behavior. The results of that inquiry have cleared Taleyarkhan of any improper behavior and he can now return to work. However, there were two notable complaints about the inquiry: no one external to Purdue was on the committee, and the complaints of faking data were not addressed by the committee at all. Despite this Purdue has deemed the matter closed and is moving on.

The scientific community is also trying to move on. A couple of months ago, an assistant professor at a minor college in Texas visited Taleyarkhan's lab and reported replicating his results. However, for the results to gain acceptance, they really need to be replicated in a different laboratory. Last year, theoretical and experimental work showed that the bubbles were not hot enough for fusion to occur. Now, in this week's Physical Review Letters, researchers who were attempting to replicate Taleyarkhan's work have reported a null result. Their experiment was based around a design provided by Taleyarkhan, but used a more sophisticated neutron counting scheme that was designed to only count neutrons detected during bubble collapse. From all their experimental data they found a solitary neutron that might be associated with a collapsing bubble, which gives an upper bound on neutron production some 10,000 less than the levels reported by Taleyarkhan.

Although the researchers say that they believe bubble fusion research should be pursued, it is clear that Taleyarkhan is being marginalized by the wider community. If his results are not replicated soon, Purdue may yet regret choosing an internal inquiry over a board of external experts.

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Chris Lee
Chris writes for Ars Technica's science section. A physicist by day and science writer by night, he specializes in quantum physics and optics. He Lives and works in Eindhoven, the Netherlands. Emailchris.lee@arstechnica.com